(1) Field of the Invention
This invention is concerned with improvements in or relating to a heater device for heating portions of shoe uppers prior to molding such uppers to a desired shape.
(2) Prior Art
A heater device described in our U.K. Pat. No. 39373/78 U.S. Pat. No. 4,284,874 has the temperature sensing element and controller which constitute a thermostatic control means, the sensing element being arranged so as to sense changes in temperature of the air in a chamber in which the inner form and outer band are accommodated. Furthermore, in the operation of said device, the second heating means is rendered operative, regardless of the thermostatic control member, whenever the device is operated to heat a shoe upper. Thus, the thermostatic control means is rather intended to ensure that, when the device is not in use but is nevertheless switched on, over-heating of the outer band, and thus its consequent degradation, can be avoided.
In using said device, satisfactory heating has readily been achieved with ladies' and children's shoe uppers. With men's shoes, on the other hand, because in use the time allocated to conditioning the upper in the heater device is restricted, and bearing in mind the greater heat drain from the band by the upper, which is of course of greater area, the output of the second heating means has to be significantly higher than in the case of ladies' and children's work. With heating means of larger output, however, the danger again arises of causing the band to degrade by excess heating, and the thermostatic control means, which essentially was used to enable the heater device to be left for relatively short break periods in a working shift, rather than for controlling the maximum temperature of the band, has proved insufficient therefore for protecting the band against excess heat in such circumstances. This of course arose essentially because of the wide fluctuations allowed by the thermostatic control means at either side of the control temperature set.
In sensing the temperature of the band, however, as opposed to the air within the chamber of the heater device difficulties have been found in attaching any temperature sensing element to the outer band without causing damage to the band and or the temperature sensing element without causing damage to the band when stretching occurs. In this regard, it will of course be appreciated that the silicone rubber sheet material of which the outer band is made has good stretch properties but relatively low cut growth resistance. Thus, it has been found that any cut or incision made in the material is likely to initiate tearing under stretch conditions, and further any attachment which causes the stretch properties to be varied in a localized area is likely to lead to tear in the region of the boundary between such area and the remainder of the band.
It is thus the object of the present invention to provide a heater device of the type aforementioned, wherein the temperature of the band is sensed by a temperature sensing element attached or secured thereto, but without the stretch properties of the material of the band being significantly varied and without running the risk of tearing of the band.